The taxonomic position of strains was examined through the results of DNA relatedness (S1 nuclease method) studies associated with the determination of Δ , 16S rRNA phylogenetic inferences and phenotypic characterization, including morphological, auxanographic, biochemical and physiological properties. Three genomic species were delineated on a consensus assessment. One of these species corresponded to , since strains were at least 50% related to the type strain of this species with Δ less than 7 °C. The two other species were novel genomic species II and III, which were less than 40% related to each other with Δ higher than 9 °C. A comparison of the complete 16S rDNA sequences of several representatives of genomic species II and genomic species III revealed that each of them formed a stable lineage independent of the cluster generated by strains. The genomic species differed in their maximum temperatures for growth. A correlation with the ecological origin of the bacterial samples was noticed. The heat-tolerant group I (maximum growth temperature 35–39 °C) corresponded to the symbionts of groups Brecon and HP88 and , nematodes living in warm and tropical countries, respectively. Group II (maximum growth temperature 33–35 °C) encompassed symbionts from and group NC1 of , nematodes isolated in temperate climates. Group III were bacteria isolated from human specimens. Two new species, sp. nov. (type strain CIP 105563 and sp. nov. (type strain ATCC 43950), are proposed for genomic species II and III, respectively. Species I and II can be separated into sub-groups on the basis of high DNA-DNA relatedness (more than 80% DNA binding with Δü < 1·5 °C), 16S rDNA branching and phenotypic characters. Therefore, we propose that the two species and should be subdivided into subspecies as follows: subsp. subsp. nov. (type strain ATCC 29999), subsp. subsp. nov. (type strain CIP 105564), subsp. subsp. nov. (type strain CIP 105565) and subsp. subsp. nov.


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